The field of the invention is valves for microfluidic applications, and in particular to the use of such microvalves for safe and controlled delivery of fluids from a reservoir.
Fluidic microvalves can be constructed from shape-memory alloys. For example, U.S. Pat. No. 7,260,932 teaches a fluid control pinch valve using shape memory alloy that receives a current to open or close the pinch valve. Similarly, U.S. Pat. No. 6,843,465 teaches a shape-memory wire actuated control valve, in which the shape-memory wire is connected to an electrical platform and mechanically coupled to a transfer mechanism. The actuator is actuated by conducting electrical current through the shape-memory wire causing the wire to contract and thereby actuating the transfer mechanism, which is operably coupled to the fluid control valve such that actuating and de-actuating the transfer mechanism opens and closes the valve. U.S. Pat. No. 6,742,761 teaches a poppet valve that is used for opening and closing a miniature latching valve by means of an actuator mechanism that includes a shape-memory alloy wire. The change in shape of the shape-memory alloy wire causes the poppet to either move toward or away from the valve seat, thereby either closing or opening the valve. U.S. Pat. No. 6,840,257 teaches a proportional valve using a shape-memory alloy actuator, with a shutter axially movable from and towards a valve seat under the control of a shape-memory alloy actuating member.
Valves are a critical component of microfluidic systems. Miniaturized valves can be used in combination with miniaturized pumps to deliver pulsed and/or constant flow of microliter or nanoliter volumes of solution (or less). The valves themselves must be small and use little power to activate. Additional power can be saved by using a latching valve that does not require power to remain in any one state. Latching valves are not designed in a normally open or normally closed state; rather they can rest in either state. In drug delivery and other applications, latching valves are an important safety feature when properly configured as they prevent a direct flow path from a large reservoir to a patient in the case of a system failure.